Sputter-type penning discharge for metallic ions

ABSTRACT

An ion source in which ions of normally solid materials are easily produced. A plasma is generated in a gas adjacent the solid material from which ions are to be produced. The solid is negatively charged and the gas plasma ions bombard the solid, sputtering off ions of the solid. This is accomplished through the use of a Penning discharge with a cold cathode-type source and a centrally positioned and negatively charged dynode upon which the solid material is mounted, the dynode being electrically connected to the cathode and provided with an exit slit through which the metallic ions are extracted from plasma potential.

1 United States Patent Inventor Basil F. Gavin [56] References Cited Berkeley, Calif- UNITED STATES PATENTS P M 806549 2,883,580 4/1959 Kilpatrick 315/111 Filed Mar. 12, 1969 Patented Feb. 23, 1971 I FOREIGN PATENTS Assignee the United States of America as represented 829,783 3/1960 Great Britain 204/298 by the United States Atomic Energy Primary Examiner-Raymond F. Hossfeld Comrnlssion Attorney-Roland A. Anderson ABSTRACT: An ion source in which ions of normally solid materials are easily produced. A plasma is generated in a gas SPUTTER'TYPE PENNING DISCHARGE FOR adjacent the solid material from which ions are to be i ig i produced. The solid is negatively charged and the gas plasma 8 Chums rawmg ions bombard the solid, sputtering off ions of the solid. This is U.S. Cl 315/111, accomplished through the use of a Penning discharge with a Int. Cl ..H05b 31/26 Field of Search 204/298; 250/41.9 (ISB) (ISE); 313/63, 230; 315/1 11 cold cathode-type source and a centrally positioned and negatively charged dynode upon which the solid material is mounted, the dynode being electrically connected to the cathode and provided with an exit slit through which the metallic ions are extracted from plasma potential.

PATENTED FEB23I97I 3,566,185

EXTRACTOR SUPPLY INVENTOR. BASIL F GAVIN BY W ATTORNEY Slill'lTEllt-TYFFE L ENNENG lIllSt'Jl-HARGE FOR METALLEC lONS BACKGROUND OF THE INVENTION The invention described herein was made in the course of, or under, Contract No. W-74C5-ENG-48, with the United States Atomic Energy Commission.

Electron discharge devices for electronically bombarding materials are well known in the prior art. However, much effort has been directed to eliminating the problems of the prior known devices associated with vaporizing materials at high temperature, based on the possibility of introducing sputtered atoms into an energetic, dense electron stream at a point where extraction in ionic form were physically feasible.

SUMMARY OF THE INVENTION The above-mentioned problems have been solved by this invention by the utilization of the Penning or oscillating electron discharge, and in particular, with a cold cathode-type source, whereby sputtered atoms are introduced into an energetic, dense electron stream at a point where extraction in ionic form is physically feasible. Since the periphery of the plasma column, or electron stream in a gas, takes on a potential close to the most positive potential of the system, a negatively charged cylinder (dynode) made of desired material and containing the solid material to be ionized is inserted in the system and is bombarded by those ions exiting the plasma boundary. These ions are accelerated to full are potential by electrically tying the dynode to the cathode, or to some fraction of the are potential. These ions sputter close to their own number of metallic ions of the material into the arc and in turn serve to counter balance the greater ion loss evident when the dynode is at cathode potential (negative). The metallic ions produced are extracted from plasma potential by fitting the dynode with anexit slit through which the ions are driven by the negative potential on the dynode.

Therefore, it is an object of this invention to provide a discharge device for readily obtaining ions directly from solid material.

A further object of the invention is to provide a means for readily obtaining ions directly from solid materials by utilizing an oscillating electron discharge coupled by a cold cathodetype source and a negatively charged dynode containing the solid material.

Another object of the invention is to provide an ion source which introduces sputtered atoms into an energetic, dense electron stream at a point where extraction in ionic form is physically feasible, thus avoiding the prior problems associated with vaporizing materials at high temperature.

Other objects of the invention will become readily apparent from the following description and accompanying drawing.

BRIEF DESCRlPTlON OF THE DRAWING The single Flt is a cross-sectional view of an embodiment of the invention with the electrical circuitry therefor shown schematically.

DESCRlPTlON OF THE EMBODIMENT The embodiment of the invention illustrated in the drawing comprises a cylindrically shaped dynode ill having an enlarged section ill including a flanged end portion ill and an aperture ll extending therethrough within which is mounted a piece of solid material 1?. to be ionized, said material being provided with aperture l3 extending therethrough and having a slit i l in the side thereof, for example, it inch by 0.050 inch, which provides fluid communication between aperture 113 and the exterior thereof. For example, dynode ll) may be constructed of aluminum, while the material l2 to be ionized may be beryllium or calcium. insulation members 15 and in having corrugated chambers 17 and 18, respectively, therein are secured to dynode it) such that chambers 17 and 18 are in fluid communication with aperture l3 of material 12. Anodes l9 and 2d are mounted respectively on insulation members and lo, the anodes being provided with central passageways 2i and 221, respectively. insulator members 23 and 2 2i having respective cavities 25 and 26 are mounted on anodes l9 and 2b in spaced relation with insulatlon members 15 and 16 and function to support, in spaced relationship with anodes l9 and Ell, cathodes 27 and 28, which are, for example, constructed of copper with titanium inserts 2'7 and 28' therein. insulation members 15 and 16 and insulator members 23 and 2% may, for example, be a ceramic, while anodes l9 and 2% may be constructed of stainless steel. Cavities 25 and 26, anode passageways 2i and 22, chambers 17 and 18 and aperture 13 of material 12 form a chamber or cavity for support gas 29 supplied via gas inlets 30 and discharged through narrow slit M as described hereinafter. The support gas 29 may, for example, be nitrogen or argon or other suitable gas.

As shown schematically, anodes l9 and 20 are electrically connected to the positive terminal of an are power supply 31 by leads 32 and 33, while the cathodes Z7 and 23 are con nected to the negative terminal of power supply 33 via leads 34, 35 and 36. An ammeter 37 is positioned between leads 34 and 35 across a resistor. 3b in lead 34, while a voltmeter 39 is positioned between leads 32 and 35 across a resistor 40 and in series with a resistor 41. Cathode 28 is electrically connected to a switch terminal 42 via a lead 43, resistor 44, a switch 45 functioning to selectively interconnect terminal 42 with dynode 10 via a lead 46. Switch 45, for example, may be a lower internal impedance screen grid tube.

Positioned within the flanged end portion 11 of dynode l0 and in spaced relation to slit 14 of material i2 is a hollow extractor electrode 47. An extractor power supply 48 is electrically connected to arch power supply 31 via positive terminals thereof, electrode 47 being electrically connected to power supply 48 as indicated by lead til. Extractor electrode 47 may, for example, be constructed of stainless steel.

As indicated by the arrow legended B in the drawing, a magnetic field is supplied, by an apparatus not shown, to produce the Penning or oscillating electron discharge within the above described apparatus as known in the art.

in operation, with the anodes l9 and 20 and 20), 27 and 28 connected to arc power supply 3i and operating in the magnetic field B, and with switch 45 closed thus connecting dynode 10 to the negative terminal of arc power supply 3i whereby material 12 is negatively charged with support gas 29 supplied via inlet 30, and with extractor electrode 47 connected to extractor power supply 48, the periphery of a plasma column, formed within support gas chamber by the Penning or oscillating electron discharge, as known in the art, takes on a potential close to the most positive potential of the system (anodes l9 and 20), negatively charged cylinder or dynode ill makes the material 12 attached thereto negatively charged which will be bombarded by those ions exiting the plasma boundary. These ions can be accelerated to full are potential, or some fraction thereof, due to the electrical connection of the dynode id to the cathodes Z7 and 28. These ions sputter close to their own number of metallic ions of the material l2 into the arc and in turn serve to counter balance the greater ion loss evident when the dynode All is at cathode potential (negative). The metallic ions produced are extracted from the plasma potential through the slit id in material 12 by the extractor electrode d7, thereby producing a beam of metallic ions, indicated at 5% which for example, can be utilized in a linear accelerator, such as the llilac (high linear accelerator).

It has thus been shown that this invention provides an apparatus or ion source in which ions of normally solid material are easily produced, this being done by generating a plasma in a gas adjacent the solid material from which ions are to be produced, the material being negatively charged, the gas plasma ions bombarding the solid, sputtering off ions of the solid which are extracted from the plasma.

While a specific embodiment of the invention has been illustrated and described, changes and changes will become apparent to those skilled in the art, and it is intended to cover in the appended claims all such modifications and changes as come within the spirit and scope of the invention.

lclaim:

1. An apparatus adapted for operation in a magnetic field to produce an oscillating electron discharge for producing a beam of ions from a normally solid material comprising: a dynode means having secured thereto a material from which the ions are to be produced, said material having an opening therein, a pair of anode means insulatively spaced from said dynode means and having openings therethrough, a pair of cathode means insulatively spaced from said anode means, a support gas chamber defined by said openings in said material and anode means and space between said anode means and said dynode and cathode means, means for maintaining support gas in said chamber, electrical circuitry means for provid ing said anode means with a positive potential and said cathode and dynode means and said material with a negative potential, said material additionally being provided with a slit therein for providing fluid communication between said opening therein and the exterior thereof through which ions sputtered from said material are discharged, and extractor circuit means having an electrode thereof positioned adjacent said material slit for providing an extracting potential on ions sputtered from said material.

2. The apparatus defined in claim 1, additionally including switch means intermediate said dynode means and said cathode means for selectively electrically isolating or connecting said dynode means with respect to cathode means.

3. The apparatus defined in claim 1, additionally including a hollow insulating member positioned between said dynode means and each of said anode means, and a hollow insulator member positioned between said anode means and said cathode means, the hollow interior of said insulating members and said insulator members forming a portion of said support gas chamber.

4. The apparatus defined in claim 1, wherein said support gas maintaining means is located adjacent said anode means.

5. The apparatus defined in claim 1, wherein said support gas is an inert gas.

6. The apparatus defined in claim 1, wherein said dynode means is constructed of aluminum.

7. The apparatus defined in claim 1, wherein said anode means are constructed of stainless steel.

8. The apparatus defined in claim 1, wherein said cathode means are constructed of copper with a titanium insert therein, said insert being exposed in spaced relationship with said anode means. 

2. The apparatus defined in claim 1, additionally including switch means intermediate said dynode means and said cathode means for selectively electrically isolating or connecting said dynode means with respect to cathode means.
 3. The apparatus defined in claim 1, additionally including a hollow insulating member positioned between said dynode means and each of said anode means, and a hollow insulator member positioned between said anode means and said cathode means, the hollow interior of said insulating members and said insulator members forming a portion of said support gas chamber.
 4. The apparatus defined in claim 1, wherein said support gas maintaining means is located adjacent said anode means.
 5. The apparatus defined in claim 1, wherein said support gas is an inert gas.
 6. The apparatus defined in claim 1, wherein said dynode means is constructed of aluminum.
 7. The apparatus defined in claim 1, wherein said anode means are constructed of stainless steel.
 8. The apparatus defined in claim 1, wherein said cathode means are constructed of copper with a titanium insert therein, said insert being exposed in spaced relationship with said anode means. 